David Akin, QMI Agency

OTTAWA - Justin Trudeau's Liberals had a breakthrough night in four federal byelections held Monday, mostly at the expense of Thomas Mulcair's NDP.

The Liberals stole one riding from the NDP in downtown Toronto, held a another riding in Toronto, and were a reasonably strong second to the Conservatives in two Alberta ridings.

Since becoming his party's leader last year, Trudeau has now stolen a seat from the Conservatives -- that was Labrador last year -- and the New Democrats -- stealing the riding Monday night in downtown Toronto that had been held by Olivia Chow.

Chow, the widow of former NDP leader Jack Layton, resigned her seat in the House of Commons to run for mayor of Toronto.

Meanwhile, in the northeastern Alberta riding of Fort McMurray-Athabasca, Liberal Kyle Harrietha put up a decent challenge to Conservative David Yurdiga in a riding that has returned conservative MPs since 1968. Yurdiga, a municipal politician in the region, will succeed Brian Jean.